This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. We will attempt to validate the Brochner-Mortenson formula [Brochner-Mortensen 1972] for determining the GFR in adult men with HIV infection and to define the two most appropriate time points for use of this formula with the plasma clearance of iohexol. With the method validated, the main outcome in this study will be the rate of decline in GFR, as assessed at two time points approximately 3 years apart. The primary goal of this study is to determine the whether HIV infection and treatments for it are risk factors for a more rapid decline in kidney function in men enrolled in the MACS.